The invention relates to the field of communication security, and more particularly to the field of security of communications using an orthogonal frequency division technique.
One drawback of asymmetrical digital subscriber line (ADSL) technology is that communications using conventional ADSL technology are not private. Typically, all subscribers to a service provider are connected to a single local area network (LAN) at the service provider""s central office. Therefore, any transmission between a subscriber and the central office LAN is potentially available to any other subscriber. Using conventional ADSL technology, all local transmissions on a subscriber""s LAN are sent to the central office and back to the subscriber""s LAN, making even these local transmissions potentially available to other subscribers.
Prior approaches to increasing privacy in an ADSL system include adding switches and routers to the service provider""s LAN to segment subscribers"" LANs from one another, and adding a router to a subscriber""s LAN to restrict local traffic to that LAN. However, these approaches increase the hardware requirements of the ADSL system and provide security only through isolation.
Therefore, a novel approach to providing security for a transmission of information that can be used in an ADSL system has been developed.
A method for providing security for a transmission of information through a plurality of frequency orthogonal subchannels is disclosed. The information is divided into a plurality of data subblocks. Each data subblock is assigned to one of the frequency orthogonal subchannels using a permutation cipher. A baseband signal representing a key to the permutation cipher is spread over a frequency spectrum for transmission with the information. This frequency spectrum comprises at least two of the frequency orthogonal subchannels.